Hydraulic power unit for a doubleacting cylinder



Feb. 4, 1969 'r. M. WILLGRUBS ETAL 4 HYDRAULIC POWER UNIT FOR A DOUBLE'ACTI ING CYLINDER Filed Jan. 25, 1967 Shee't of 5 COOLER INVENTORS THEODORE M.W|LLGRUBS W LLIAM H. SMITH TOM LEARMONT ATTORNEY Feb.

T. M. WILLGRUBS ETAL HYDRAULIC POWER UNIT FOR A DOUBLE-ACTING CYLINDER Filed Jan. 25, 1967 Sheet INVENTORS THEODORE M.WILLGRUBS WILLIAM H. SMITH TOM LEARMONT ATTORNEY Feb. 4, 1969 1-. M. WILLGRUBS ETAL 3,425,574

HYDRAULIC POWER UNIT FOR A DOUBLE-ACTING CYLINDER Sheet Filed Jan. 25, 1967 INVENTORS.

BS WILLIAM H SMITH TOM L EARMONT ATTORNEY United States Patent 3,425,574 HYDRAULIC POWER UNIT FOR A DGUBLE- ACTING CYLINDER Theodore M. Willgrubs, South Milwaukee, William H. Smith, Greendale, and Tom Learmont, Milwaukee, Wis., assignors to Bucyrus-Erie Company, Milwaukee, Wis., a corporation of Delaware Filed Jan. 25, 1967, Ser. No. 611,663 US. Cl. 214-435 12 Claims Int. Cl. Eti2f3/30;F15h 15/18 ABSTRACT OF THE DISCLOSURE An hydraulic power unit drives a double-acting cylinder that is mounted to crowd the dipper handle of a power shovel. In the power unit, an electric motor simultaneously drives six reversible pumps to pump fluid for the cylinder bore. Driven in one direction, all six pumps pump fluid to the blind end of the bore, while two of them meter fluid from the rod end of the bore. Driven in the opposite direction, the two pumps pump fluid to the rod end, While all six pumps meter fluid from the blind end. Auxiliary circuitry is also disclosed.

Background of the invention In its broadest aspect, the present invention is an hydraulic power unit including a fluid reservoir, pumps, a prime mover for driving the pumps and hydraulic circuitry specifically designed and adapted for driving a double-acting hydraulic cylinder, which performs work in both directions. In its narrower aspect, the invention is such a power unit especially designed and adapted for .use in excavators, and, specifically, crowd mechanisms of power shovels.

In the known prior art, there are, generally, two types of crowd mechanisms for power shovels: gear and rack crowd mechanisms, and rope crowd mechanisms. Other types of excavators use levers to achieve a crowd type movement of a bucket, and the levers may be actuated by hydraulic cylinders, but this is a different type of action. Prior art hydraulic power units for driving doubleacting cylinders have usually relied upon intricate valving to meter fluid flow and to apportion fluid flow properly between the large volume blind end side of the piston and the comparatively small volume rod end side of the piston. Such power units are unable to prevent loss of control of an overhauling load and valves are not available that are capable of controlling the fluid flow involved in excavator applications.

Summary of the invention The present invention relates to an hydraulic power unit for a double-acting hydraulic cylinder having a blind end bore and a rod end bore on opposite sides of a reciprocatory piston, wherein a first pump means is connected to control the flow of hydraulic fluid to and from the blind end bore, and a second pump means is connected to control the flow of hydraulic fluid to and from the rod end bore So that reciprocating movement may be imparted to said reciprocatory piston; and the invention also relates to a crowd mechanism for a power shovel wherein said double-acting cylinder driven by said power unit imparts crowd action to a dipper handle of said power shovel.

It is the principal object of the present invention to provide an hydraulic power unit that is sufficiently rugged, reliable, self-suflicient, safe and economical for driving a double-acting hydraulic cylinder on a power shovel or other excavator. Also, it is an object of the present invention to provide a power unit for a double-acting cylinder 3,425,514 Patented Feb. 4, 1969 control of the double-acting cylinder in both directions at all times. According to the invention, either constant displacement pumps driven by a variable speed motor or variable displacement pumps driven by a constant speed motor can be used. In addition, the present invention provides an auxiliary circuit for the cooling, filtering, emptying and filling of hydraulic fluid for the power unit so that the power unit can be self-sufiicient and easily maintained, even in remote excavating sites.

In the attached drawings and the following description the best mode presently contemplated for carrying out the invention is set forth. The manner and process of making and using the invention is described below in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the invention. It should be emphasized, however, that the subject matter regarded as the invention is not limited solely to the here described embodiment of it, but rather includes everything falling within the claims set forth at the conclusion of this specification.

Brief description of the drawings FIG. 1 is a schematic diagram of a preferred embodiment of the power unit of the present invention.

FIG. 2 is a side view in elevation of a power shovel utilizing the power unit of the present invention in its crowd mechanism.

FIG. 3 is a side view in elevation, partially in section, of the dipper handle and saddle block of the power shovel shown in FIG. 2.

FIG. 4 is a side elevation in section of the dipper handle shown in FIG. 2 having a double-acting hydraulic cylinder mounted in it as a crowd drive.

Description of the preferred embodiment Referring now specifically to the drawings, FIG. 1, which shows a schematic diagram of a preferred embodiment of the power unit of the present invention as applied to provide the crowd action of a power shovel, the power unit has four reversible, rotary vane, fixed displacement hydraulic pumps 1, 2, 3 and 4 and two, fixed displacement, reversible, rotating axial piston type pumps 5 and 6. Each of the four vane pumps 1-4 in the commercial embodiment will deliver 106 gallons per minute at 1800 rpm, and the piston pumps 5 and 6 deliver 118 gallons per minute at 1200 rpm. The use of fixed displacement pumps 1 through 6 in this embodiment is largely an economy measure. Fixed displacement pumps are less expensive than variable displauement pumps; and, what is more, much of the associated equipment was on hand so that the cost of converting from a rope crowd to an hydraulic crowd is further minimized by using fixed displacement pumps. However, the invention, in light of known prior art, contemplates the use of variable displacement pumps also.

The pumps 1-6 drive a double-acting hydraulic cylinder 7. The double-acting hydraulic cylinder 7 is made up of a cylindrical bore 8 in which a piston 9 is reciprocably mounted. A piston rod 10 extends axially from one end of the piston 9 through a rod end 11 of the cylinder bore 8. On the opposite side of the piston 9 from the rod end 11 is a blind end 12 of the cylinder bore 8. The dimensions of the cylinder 7 are such that rate of change of volume of the blind end 12 to the rod end 11 as the piston moves is 2.78 to 1, or roughly 3 to 1; and, specifically, the bore 8 is 10 inches in diameter and the rod 10 is 8 inches in diameter. One passage 113 communicates with the blind end 12 of the bore 8, and a second passage 14 communicates with the rod end of the bore 8.

An hydraulic fluid reservoir 15 is mounted above the pumps 1-6 to contribute a pressure head to the total discharge pressure of the power unit to the cylinder 7, and by that amount reduce the differential pressure-required of the pumps 1-6. A main working line 16, which has both of its ends 17 and 18 terminating in the reservoir 15, is made up of three sections 19, 20 and 21. The first section 19 of the main working line 16 extends from one end 17 in the reservoir 15 down to a check valve 22. Conductors 23 and 24 from one side of the vane pumps 1 and 2, respectively, join the first section 19 of the main working line 16. A pair of drain lines 25 and 26 from the piston pumps and 6, respectively, empty directly into the reservoir 15. A manually operated valve 27 in the first section 19 of the main working line 16 provides a vacuum relief for letting air into the first section 19 when the system is being drained, The second section 20 of the main Working line 16 extends from the other end 18 in the reservoir 15 to a check valve 28, and conductors 29 and 30 from one side of the other tWo vane pumps 3 and 4, respectively, join the second section 20. The second section 20 also has a manual valve 31 connected into it for allowing air into the second section 20 of the main working line 16 when the system is being drained.

The third section 21 of the main working line 16 extends between the two check valves 22 and 28. Conductors 32, 33, 34 and 35 from the other sides of the vane pumps 14, respectively, and a common conductor 36 from one side of the piston pumps 5 and 6 are joined to the third section 21. A blind end working line 37 joins the third section 21 of the main working line 16 to the passageway 13 communicating with the blind end 12 of the cylinder bore 8. The third section 21 is also joined by two lines that are not active in the usual operation of the unit, viz.: an overload relief line 38 and a manual check valve 43 used in draining and filling the entire power unit.

The other sides of the piston pumps 5 and 6 are connected to a rod end working line 40, one end of which terminates in the passageway 14 communicating with the rod end 11 of the cylinder bore 8. The other end of the rod end working line 40 contains a check valve 41 and is joined to an auxiliary hydraulic system, which is described infra. The rod end working line 40 also has a. manual check valve 42 connected to it for use in draining and filling hydraulic fluid for the entire power unit. The manual check valves 42 and 43, thus, provide valve means communicating with the main working line 16 for filling and draining the power unit.

The relief line 38 extends from the third section 21 of the main working line 16 to the blind side working line 37, and it contains a low pressure relief valve 45, a pressure maintaining relief valve 46 and a check valve 47. The low pressure relief valve 45 is adjusted to open when the pressure in the relief line 38 exceeds 1100 p.s.i., and the pressure maintaining valve 46 opens at 5 p.s.i. A drain line 48, which joins with the relief line 38 at a point between the low pressure relief valve 45 and the pressure maintaining valve 46, empties into the reservoir 15. Between the low pressure relief valve 45 and the pressure maintaining relief valve 46, the relief line 38 is connected through a high pressure relief valve 49 to the rod end working line 40. The high pressure relief valve 49 is adjusted to open when the pressure in the rod end working line 40 exceeds 2550 p.s.i. A pressure operated electrical switch 50 is connected into the relief line 38 between the pressure maintaining relief valve 46 and the high and low pressure relief valves 49 and 45, respectively. The relief line 38 is also connected to a piston type accumulator 51.

A variable speed DC. motor 52 is mechanically connected through a conventional transmission (not shown) to drive the six pumps 1-6 simultaneously. Since the pumps 1-6 are constant displacement, reversible pumps, fluid flow in the power unit is controlled by varying the speed of and reversing the variable speed DC. motor, employing any of the conventional motor controls for this purpose. At somewhat greater expense, a constant speed AC. motor could be used with variable displacement pumps in a power unit of the present invention; and in this case, fluid flow control would be achieved at the pumps 16.

In addition to the main hydraulic circuit just described, there is also an auxiliary hydraulic circuit which provides temperature control for the hydraulic fluid, filling and draining of the entire power unit and a constant pressure head on the pumps 1-6. Fluid in the auxiliary circuit is circulated by a fixed displacement, rotary, internal vane, auxiliary pump 53, which is driven by a constant speed, alternating current motor 54, and which will deliver 82.5 g.p.m. at 1800 r.p.m. An auxiliary supply line 55 joins one side of the auxiliary pump 53 to the reservoir 15, and it contains a pair of parallel magnetic filters 56, which are in series with a manual control valve 57. A manual outlet valve 58 is joined to the auxiliary supply line 55 at a point between the control valve 57 and the magnetic filters 56, and a branch line 59 joins the auxiliary supply line 55 between the control valve 57 and the reservoir 15. The branch line 59 is connected to an auxiliary working line 60 through a relief valve 61 and a manual control valve 62 arranged in parallel.

One end of the auxiliary working line 60 terminates in the opposite side of the auxiliary pump 53 from the supply line 55. Coming from the pump 53, the auxiliary working line 60 contains a flow responsive electric switch 63, a pressure line filter container 64 with a dirt indicator and containing a 25 micron selection element, a manual control valve 65, and the line 60 terminates in the accumulator 51. The rod end working line 40 joins the auxiliary working line 60 between the manual shut off valve 65 and the accumulator 51 so that the auxiliary pump 53 can maintain a pressure head of 75 p.s.i. on the piston pumps 5 and 6. An outlet valve 66 is joined to the auxiliary working line 60 between the auxiliary pump 53 and the manual shut off valve 65.

A return branch 67 joins the auxiliary working line 60 between the manual shut off valve 65 and accumulator 51, and it terminates in the reservoir 15. The return branch 67 contains a pressure control relief valve 68, which is adjusted to open when the pressure in the auxiliary working line 60 exceeds 75 p.s.i. A two-position, three-way direction control valve 69 is connected into the return branch 67 of the auxiliary working line 60 in series with the pressure control relief valve 68, and it is connected to be actuated by a pilot valve 70, which is controlled by a solenoid 71. The direction control valve 69 is connected to direct the fluid flow in the return branch 67 either through a cooler 72, or a by-pass conduit 73, and back to the reservoir 15. A pilot line 74 from the pilot valve joins the rod end working line 40 between the check valve 41 and the junction of that line 40 with the auxiliary working line 60, and a drain line 75 from the pilot valve 70 joins the by-pass conduit 73.

A pair of thermally operated control contacts 77 and 78 are mounted on the reservoir 15. The low temperature contact '77 is adjusted to be actuated when the fluid temperature in the reservoir 15 reaches 75 F., and the high temperature contact 78 will be actuated when the fluid temperature in the reservoir reaches F. The low temperature contact 77 is electrically connected to energize a cooling fan (not shown) in the cooler 72 and the solenoid 71, when it is actuated; and the high temperature contact 78 is electrically connected to an electrical control circuit 79 for the entire power unit. Actually, the contacts 77 and 78 are both contained in a single thermal control switch, which is not separately represented on the drawing to avoid unnecessary complexity in the drawing.

Similarly, the pressure operated switch 50 has two ganged contacts 80 and 81, a normally closed solenoid contact 80 and a normally open cycling contact 81. The solenoid contact 80 is electrically connected to deenergize the solenoid 71 when actuated; and the cycling contact 81 is electrically connected to energize a timer 82, which is electrically connected to send periodic, timed signals to the electric control circuit 79. The flow responsive switch 63 is electrically connected to send a signal to the electric control circuit 79 when the flow of fluid in the auxiliary working line 60 is reduced below a preset, safe maximum. Since the electrical components and circuitry are not, taken alone, a part of the invention, there is no need to describe them any further.

This embodiment of the invention was created to be used as a power unit for an hydraulic crowd mechanism for a shovel. The copending application Ser. No. 563,452, filed July 7, 1966, is drawn specifically to the mechanical aspects of the hydraulic crowd mechanism, and reference may be had to it for further detail as to that aspect. FIG. 2 shows a power shovel with a turntable 90 mounted on a crawler truck 91 and supporting a cab 92 that houses the power unit, control equipment and operator, and an A-frame 93 for supporting the top end of a boom 94, the bottom end of the boom 94 being mounted on the front of the turntable 90. A dipper 95 is mounted on the front end of a dipper handle 96 which is slidably supported in a saddle block 97. The saddle block 97 is made up of a yoke 98 and a piston rod support frame 99, which projects rearwardly from the yoke 98 and encloses the back end of the dipper handle 96. The yoke 98 of the saddle block 97 is pivotally mounted to the boom 94, so as to pivot in a vertical plane, and a hoist cable 100 extends upward from a powered hoist drum 101 on the turntable 90, over a sheave 102 at the top of the boom 94 and down to a 'bail 103 on the dipper 95. The hoist cable 100 provides for the vertical, raising and lowering movement of the dipper 95. The crowd mechanism, with which this invention is associated, provides the horizontal component, or crowd, of the dippers 95 movement. In FIG. 2, the reservoir and hydraulic pumps 1-6 are visible, the variable speed DC. motor 52 for driving the pumps 1-6 is also represented and the blind side and rod side working lines 37 and 40, respectively, are shown.

The double-acting cylinder 7 is shown in greater detail in FIGS. 3 and 4. FIG. 3 shows the dipper handle 96 in the saddle block 97 with portions broken away to show the double-acting cylinder 7, the piston rod 10 and the passageway 13 through the hollow piston rod 10 for conducting hydraulic fluid to the blind end 12 of the bore 8. Also, a portion of the back end of the piston rod support frame 99 is in section to illustrate the lug 104 on the end of the piston rod 10 by which the piston rod 10 is secured to the piston rod support frame 99. The lug 104 has a relief formed in it for a fitting about the fluid passageway 13, which is a tube extending through the hollow piston rod 10 and the piston 9 to the blind end 12 of the bore 8. To minimize fluid flow resistance, two ducts 116 through the back end of the wall of the hollow piston rod 10 communicate with the fluid passageway 14 to the rod end 11 of the bore, the fluid passageway 14 being the space between the inside surface of the hollow piston rod 10 and the outside of the tube forming the fluid passageway 13. Ducts 115 communicate between the fluid passageway 14 and the blind end 11 of the bore 8.

FIG. 4 is a side elevation in section of the dipper 96 with the double-acting cylinder 7 mounted inside of it. The double-acting cylinder 7 is cushioned at both ends by means of the captive areas 105 and 106 in the rod end 11 and blind end 12 of the bore 8, respectively. A piston seal for the piston 9 is formed by two piston rings 107 and 108, and a rod seal is formed by a head 109 which is screw fitted in the end of the bore 8, although other types of fastenings are also used, and contains packing 110 about the piston rod 10 as well as a cushion seal 111.

The double-acting cylinder 7 has an end cap, center line mounting in the form of a fixed eye 112 on the blind end, through which a pin 113 in the dipper handle 96 is journaled, and as disclosed in FIG. 3, the rod has the lug 104 by which it is anchored to the saddle block 97 by a pin 114 through the back end of the crowd support frame To extend the piston rod 10, and thus the dipper handle 96, outwardly, the pumps 1-6 are driven by the electric motor 52 in such a direction that two of the vane pumps 1 and 2 pump fluid from the first section 19 of the main working line 16 through the pump conductors 23 and 24, and 32 and 33, respectively, to the third section 21 of the main working line 16, the other two vane pumps 3 and 4 pump fluid from the second section 20 through conductors 29 and 30, and conductors 34 and 35, respectively, to the third section 21 of the main working line 16. The two piston pumps 5 and 6 pump fluid from the rod end working line 40 through the common conduit 36 to the third section 21 of the main working line 16. The fluid thus pumped into the third section 21 of the main working line 16 flows through the blind side Working line 37 and the passage 13 to the blind end 12 of the bore 8 of the cylinder 7. The fluid pressure in the blind end 12 of the bore 8 forces the piston 9 towards the rod end 11 of the bore 8, thus extending the piston rod 10. If the load on the dipper is below the saddle block 97, gravity would aid the extension of the piston rod 10, with the result that if the fluid were permitted to flow freely out of the rod end 11 of the bore 8, control of the load would be lost. However, in the invention, the fluid in the rod end 11 of the bore 8 is metered through the piston pumps 5 and 6 and its flow is thus limited by the speed at which the piston pumps 5 and 6 are driven.

To retract the piston rod 10 into the bore 8 and thus to draw the dipper 95 toward the saddle block 97, the direction of rotation of the pumps 1-6 is reversed. Hydraulic fluid is then pumped by the piston pumps 5 and 6 from the third section '21 of the main working line 16 into the rod end working line 40, through the passage 14 and into the rod end 11 of the bore 8, forcing the piston towards the blind end 12 of the bore 8. Simultaneously, the vane pumps 14 pump hydraulic fluid from the blind end 12 of the bore 8 through the passage 13, the blind end working line 37 and the third section 21 of the main working line 16, and then through conductors 32, 3.3, 34 and 35, respectively, to the pumps 14, and then from the pumps 14 through conductors 23, 24, 29 and 30, respectively, to the first and second sections 19 and 20, respectively, of the main working line 16 and from the main working line 16 to the reservoir 15. If the load inthe dipper 95 is higher than the saddle block 97, gravity would aid the piston pumps 5 and 6, and if the flow of fluid from the blind end 12 of the bore 8 were unlimited, control of the load would be lost. However, the six pumps 1-6 through which the fluid from the blind end 12 of the bore 8 must flow, meter flow rate so that control of the load may be effected through the DC. motor 52.

To summarize, all six pumps 1-6 constitute pump means for the blind end 12 of the bore 8 of the double-acting cylinder 7, and only the two piston pumps 5 and 6 provide pump means for the rod end 11 of the double-acting cylinder 7. Since the six pumps have approximately equal pumping capacity, the pump means for the blind end of the bore 8 has three times the pumping capacity of the pump means for the rod end 11 of the bore 8, and this ratio coincides with the ratios of change in volume of the blind end 12 of the bore 8 to the rod end 11 of the bore 8 as the piston 9 moves through the bore 8. Due to the much greater piston area against which the fluid in the blind end 12 of the bore 8 acts, the pressure required to vane pumps, the piston pumps and 6 were selected as pump means for the rod end 11 of the bore 8, and the relatively high efficiency of vane pumps with high capacity discharge and in metering fluid flow dictated the choice of rotary vane pumps 14 to supply most of the fluid flow for the'blind end 12. However, vane pumps, gear pumps, piston pumps and others have been developed and will continue to be developed that can function in any of the positions of the six pumps 1-6 shown here. At present, cost factors dictate the choice of pumps 14 and 56, but this may change in the future. Hence, it is thought that the invention ought not to be limited to the types of pumps used.

If an overload develops during crowd movemen in either direction, breakdown is prevented by one or the other of the relief valves 45 or 49. If the overload occurs during extension in the blind end 12 of the cylinder bore 8, the resulting fluid pressure will open the relief valve 45 to the relief line 38. If the overload occurs during retraction in the rod end 11 of the cylinder bore 8, the resulting fluid pressure will open the relief valve 49 to the relief line 38. From the relief line 38, the fluid may flow back to the rod end 11 or the blind end 12 of the cylinder bore 8, as needed, through check valves 41 or 47, respectively, or it may return to the reservoir 15 through relief valve 68, as the pressure levels of the system demand. Meanwhile, the relief valve 46 ensures sufficient back pressure in the relief line 38 to actuate the pressure switch 58. The relief valve 46 performs the additional function of isolating the relief valves 45 and 49 from back pressure from the auxiliary pump 53, which could otherwise interfer with the proper operation of the relief valves 45 and 49.

To operate efficiently, these piston pumps 5 and 6 should have a pressure head of from 50 to 100 pounds flowing into them. In the present invention, this pressure head is provided in part by mounting the reservoir 15 above the pumps 16, but mostly by the auxiliary system. The auxiliary pump 53 is driven by the constant speed, ten horsepower alternating current motor 54 to draw fluid from the reservoir 15 through the auxiliary supply line 55, the control valve 57 and the magnetic strainers 56 to the auxiliary working line 60. The fluid in the auxiliary working line 60 flows through the return line 67 and back to the reservoir 15, either through the cooler 72 or the bypass conduit 73. However, the fluid in the auxiliary working line 60 also enters the main working system through the rod end working line 40 and through the relief line 38 to the blind end working line 37. During normal operation, there is no flow of fluid from the auxiliary system into the main Working system through those channels; but instead, the fluid from the auxiliary system maintains a constant pressure of 75 pounds on the fluid in the main working system. The 75 pound pressure level is established by the relief valve 68 in the return line 67.

The auxiliary system also provides temperature control for the hydraulic fluid for the working system by continually circulating the fluid from the reservoir 15 through the supply line 55, the pump 53, the auxiliary working line 60, the return line 67, the cooler 72 and back to the reservoir 15. When the fluid temperature is less than 75 Fahrenheit, the three-way valve 69 shunts the fluid around the cooler 72 through the by-pass conduit 73; but when the fluid temperature in the reservoir 15 reaches 75, the low temperature contacts 77 are actuated to energize the solenoid 71 and a cooling fan (not shown) in the cooler 72. The solenoid 71 actuates the pilot valve 70 which controls the directional valve 69 to direct the fluid to the cooler '72. If the fluid in the reservoir 15 reaches 150 Fahrenheit, the high temperature contacts 78 are closed and this signals the electrical control system 79 to shut down the main system of the power unit by deenergizing the DC. motor 52. When the motor 52 is shut down, a brake (not shown) automatically sets on the dipper handle 96 as a safety measure.

If the operator of a power unit of the present invention were to leave the double-acting cylinder in either of its extreme positions, viz., with the piston 9 either hard against the rod end 11 of the bore 8 or against the blind end 12 of the bore 8, with the pumps continuing to attempt to drive the piston 9 further into the extreme position, the system would soon become overheated and break down. To avoid any damaging results, the cycling contact 81 is provided on the pressure operated switch 50. The existence of that dangerous condition would first manifest itself in excessive pressure in the system, causing the break over of one, or the other, or both of the pressure relief valves 45 and 49, and actuating the pressure operated electric switch 50.

When the pressure switch 50 is actuated, the solenoid contact 80 is opened and the cycling contact 81 is closed. The opening of the solenoid contact 80 deenergizes the solenoid 71 which actuates the pilot valve to operate the directional control valve 69 so that the path through the cooler 72 is closed and the path through the by-pass 73 is opened. Thus, the overflow fluid from the main system can be shunted rapidly from the relief line 38 back to the reservoir 15 without damaging the cooler 72.

When the cycling contact 81 of the pressure operated switch 50 is closed, a signal is sent to the timer 82, energizing the timer 82. After the cycling contact 81 has remained closed for ten seconds, the timer 82 sends a signal to the electric control circuit 79 which deenergizes the variable speed DC. motor 52. Meanwhile, the fluid bleeding through the restricted drain line 48 to the reservoir 15 reduces the pressure sufficiently to restore the pressure switch 50 to its normal condition. With the closing of the cycling contact 81 of the pressure switch 59, the DC. drive motor 52 is energized, and the closing of the solenoid contact restores fluid circulation through the cooler 72. If the operator does not correct the overload condition, the cycle just described, beginning with the opening of one of the relief valves 45 or 49, will be repeated. When the variable speed DC. motor 52 is attempting to drive the pumps 1-6 in such circumstances, it emits a characteristic loud growling noise so that the cycling of the system to generate that noise at ten second intervals is bound to alert the operator to the condition. Such a condition might well arise when a unit of the present invention is used in an excavator and the dipper is lowered to the ground and extended to its furthest limit during an interval in normal operation. If the operator were to leave his controls at this point, an overload condition could develop resulting in the cycling of the system calling the operators attention to the situation.

The auxiliary system already described performs three additional functions, to wit: draining the system, precharge filtering of hydraulic fluid, and filling of the system with hydraulic fluid. To drain hydraulic fluid from the system as one would do in changing the fluid or for other maintenance purposes, first close the control valve 57 in the auxiliary supply line 55 and the manual control valve 65 in the auxiliary working line 60. Then open the manual control valve 62 in the branch line 59 and the manual outlet valve 58 in the auxiliary supply line 55, leaving the manual outlet valve 66 in the auxiliary working line 60 closed. Next, connect the manual check valves 42 and 43, shown at the bottom of the drawing, to the manual outlet valve 58 in the auxiliary supply line 55, and open the manual check valves 42 and 43. Then by energizing the constant speed auxiliary AC. motor 54 to drive the auxiliary pump 53, fluid will be pumped out of the system through the manual check valves 42 and 43 and into the auxiliary system through the outlet valve 58. From the outlet valve 58, the fluid is pumped through the magnetic filters 56, the pump 53, the filter 64 in the auxiliary working line 60, through the manual control valve 62 and the auxiliary supply line 55 back to the reservoir 15. The oil may then be drained from the reservoir 15 in the conventional manner.

Before charging the system with new fluid, it is highly desirable, if not essential, to filter that fluid; and the auxiliary system of the present invention provides a means for doing so in a remote location without the use of any extra equipment. First close the manual control valve 57 in the auxiliary supply line 55, the manual control valve 62 in the branch line 59 and the manual control valve 65 in the auxiliary working line 60. Then open the manual outlet valves 58 and 66 in the auxiliary supply line 55 and the auxiliary working line 60, respectively, and connect the manual outlet valves 58 and 66 into the drum of fluid (not shown). When the auxiliary pump 53 is then driven by the auxiliary motor 54, fluid will be pumped out of the drum (not shown) through the manual outlet valve 58, the magnetic filters 56, the auxiliary pump 53, and the filter 64 in the auxiliary working line 60 back to the drum (not shown) through the outlet valve 66. After the fluid has been filtered, it may be introduced into the system.

The filtered hydraulic fluid is pumped into the empty reservoir 15. The following valves are closed: the manual outlet valve 58 in the auxiliary supply line 55, the manual control valve 62 in branch line 59, and the manual control valve 65 in the auxiliary working line 60. The manual control valve 57 and auxiliary supply line 55 and the manual outlet valve 66 in the auxiliary working line 60 are open. The manual outlet valve 66 is next connected to the manual check valves 42 and 43, and the auxiliary motor 54 is energized to drive the auxiliary pump 53. Fluid is pumped from the reservoir 15 through the auxiliary supply line 55, the manual control valve 57, the magneitc filters 56, the pump 53, the filter 64 in the auxiliary working line 60, and through the manual outlet valve 66 and the manual check valves 42 and 43 into the main systems.

The foregoing description shows that a hydraulic unit embodying the present invention is a complete, self-contained power unit capable of providing all the functions required for its own operation and maintenance in a remote site without the usual additional supporting equipment. It is an inherently, relatively trouble-free and reliable unit capable of performing in all climates with extraordiuarily accurate control. While these advantages suit it admirably for use as a power unit for dllVlllg a hydraulic crowd mechanism of an excavator, it is obvious that such advantages are also desirable in many other uses both related and unrelated to excavators. Therefore, the invention cannot be limited to the specific embodiment shown but rather is set forth in the claims that follow.

We claim:

1. An hydraulic power unit for a double-acting hydraulic cylinder comprising the combination of:

a double-acting hydraulic cylinder having a bore, a piston mounted in said bore and defining a blind end of said bore on one end of said piston and a rod end of said bore on the other end of said piston, a passage communicating with said blind end of said bore, and a passage communicating with said rod end of said bore;

a reservoir of hydraulic fluid;

a first pump means connected between said blind end of said bore and said reservoir to pump hydraulic fluid into said blind end of said bore and to meter hydraulic fluid out of said blind end of said bore;

a second pump means connected between said rod end of said bore and said blind end of said bore to pump hydraulic fluid alternately into said blind end of said bore and said rod end of said bore and to meter hydraulic fluid out of said rod end of said bore;

said first and second pump means having pumping capacities approximately proportional to the rates of change of volume of said blind end of said bore and said rod end of said bore as said piston moves in said bore and said first and second pump means being operated at a fixed proportion of said pumping capacities;

and a motor connected to simultaneously drive said pump means. i

2. An hydraulic power unit as set forth in claim 1 wherein:

said first and second pump means generate discharge pressures approximately proportional to the cross sectional areas of said blind end of said bore and said rod end of said bore respectively to exert approximately equal force on said ends of said piston.

3. An hydraulic power unit as set forth in claim 2 wherein:

an auxiliary pump is connected between said reservoir and said first and second pump means to maintain a positive pressure head on said pump means.

4. An hydraulic power unit as set forth in claim 3 wherein:

said auxiliary pump is also connected to a cooler to circulate said hydraulic fluid from said reservoir through said cooler and back to said reservoir in response to the temperature of said hydraulic fluid.

5. An hydraulic power unit as set forth in claim 3 wherein:

a filter is connected in a line to said! auxiliary pump;

and an outlet valve is connected to said line to permit fluid to be pumped by said auxiliary pump into said outlet valve and through said filter to said reservoir.

6. An hydraulic power unit as set forth in claim 1;

wherein:

a relief valve is connected to said blind end of said bore to prevent overload;

and a second relief valve is connected to said rod end of said bore to prevent overload.

7. An hydraulic power unit as set forth in claim 1 wherein:

said first and second pump means are reversible fixed displacement pumps;

and said motor is a variable speed reversible electric motor.

8. An hydraulic power unit as set forth in claim 4 wherein:

said motor driving said first and second pump means is a variable speed motor;

an electric motor drives said auxiliary pump;

a flow responsive electric switch is connected to be actuated by hydraulic fluid discharge of said auxiliary pump and to cause said variable speed motor and said electric motor to be deenergized when said discharge is below a preset minimum;

a temperature control switch is connected to be actuated by the temperature of the hydraulic fluid in said reservoir and to cause said fluid to be circulated through said cooler when said temperature exceeds a preset low maximum and to cause said variable speed motor to be deenergized when said temperature exceeds a preset high maximum.

9. A power unit as set forth in claim 3 wherein:

first valve means communicate with main working lines on a blind end side and a rod end side of said cylinder for draining and filling said power unit;

second valve means is connected to a discharge side of said auxiliary pumps;

said second valve means is adapted to be connected to said first valve means;

and said auxiliary pump is operable to fill said power unit with hydraulic fluid from said reservoir through said first and second valve means.

10. A crowd mechanism comprising the combination a power shovel having a boom, and a dipper on an end of a dipper handle reciprocably supported on said boom;

and a power unit as set forth in claim 1 with said double-acting cylinder being connected to reciprocate said dipper handle.

11. A crowd mechanism as set forth in claim 10 wherein:

said double-acting cylinder has a single piston rod on said piston and extending axially through said rod end of said bore and out of said bore;

said passages communicating with said rod end of said bore and said blind end of said bore extend axially through said piston rod;

and said piston rod is mounted in fixed relationship to said boom and said cylinder is mounted to reciprocate with said dipper handle.

12. A crowd mechanism as set forth in claim 11 wherein:

said second pump means is made up of two reversible fixed displacement reciprocating piston pumps;

said first pump means is made up of four reversible fixed displacement rotating vane pumps connected between said blind end of said bore and said reservoir and said two reversible fixed displacement reciprocating piston pumps connected between said rod end of said bore and said blind end of said bore; and said motor is a variable speed reversible direct current motor connected in common to drive both said first pump means and said second pump means.

References Cited UNITED STATES PATENTS HUGO O. SCHULZ,

Primary Examiner.

US. Cl. X.R. 

